Spatiotemporal characterization of the field-induced insulator-to-metal transition

Many correlated systems feature an insulator-to-metal transition that can be triggered by an electric field. Although it is known that metallization takes place through filament formation, the details of how this process initiates and evolves remain elusive. We use in-operando optical reflectivity to capture the growth dynamics of the metallic phase with space and time resolution. We demonstrate that filament formation is triggered by nucleation at hotspots, with a subsequent expansion over several decades in time. By comparing three case studies (VO2, V3O5 and V2O3), we identify the resistivity change across the transition as the crucial parameter governing this process. Our results provide a spatiotemporal characterization of volatile resistive switching in Mott insulators, key for emerging technologies such as optoelectronics or neuromorphic computing.

Resistance Temperature Detectors Fabricated via Dual Fused Deposition Modeling of Polylactic Acid and Polylactic Acid/Carbon Black Composites

Planar-type resistance temperature detectors (P-RTDs) were fabricated via fused deposition modeling by dual nozzle extrusion. The temperature-sensing element of the fabricated sensor was printed with electrically conductive polylactic acid/carbon black (PLA/CB) composite, while the structural support was printed with a PLA insulator. The temperature-dependent resistivity change of PLA/CB was evaluated for different stacking sequences of PLA/CB layers printed with [0°/0°], [−45°/45°], and [0°/90°] plies. Compared to a PLA/CB filament used as 3D printing source material, the laminated structures exhibited a response over 3 times higher, showing a resistivity change from −10 to 40 Ω∙cm between −15 and 50 °C. Then, using the [0°/90°] plies stacking sequence, a P-RTD thermometer was fabricated in conjunction with a Wheatstone bridge circuit for temperature readouts. The P-RTD yielded a temperature coefficient of resistance of 6.62 %/°C with high stability over repeated cycles. Fabrication scalability was demonstrated by realizing a 3 × 3 array of P-RTDs, allowing the temperature profile detection of the surface in contact with heat sources.

Evaluation of p-Type 4H-SiC Piezoresistance Coefficients in (0001) Plane Using Numerical Simulation

A numerical simulation of p-type 4H-Silicon Carbide (4H-SiC) piezoresistance coefficients in (0001) plane evaluation is shown in this study. A 4H-SiC material has outstanding material characteristics of wide band-gap of 3.26 eV and high temperature robustness. However, many material properties of 4H-SiC material are still unknown, including piezoresistance coefficients. Piezoresistive effect is resistivity change when mechanical stress is applied to the material. Piezoresistance coefficients express the magnitude of this effect, important for designing a mechanical stress sensor. In this study, reported piezoresistance coefficients of p-type 4H-SiC in (0001) plane is evaluated based on numerical simulation. The simulated results of Gauge Factor (GF) values (determined by (ΔR/R)/ε (R is the resistance and ε is the strain of material)) well matched to the theoretical GF values (determined by πE (π is the piezoresistance coefficient and E is Young’s modulus of the material)), shows that reported piezoresistance coefficients are reliable. Also, the internal mappings of piezoresistive effect from the numerical simulation are shown, useful to understand piezoresistive effect which is difficult to see by experimental results.

Electrode for Wearable Electrotherapy

An electrode is a fundamental element used in many electrotherapy devices. This work presents a novel dry electrode made from carbon and silicone rubber materials for wearable electrotherapy applications. The electrode was mixed using a speed mixer and fabricated using stencil printing. This paper investigates the resistivity change of the electrode under the pressure from 0 mmHg to 32.4 mmHg; and the skin–electrode impendence with the current frequency from 20 Hz to 10,000 Hz. The resistivity of the novel dry electrode is 24.6 ± 1.5 Ω∙m when the pressure on electrode is 17.7 mmHg. The skin–electrode impedance reduced from 1001.6 Ω to 145.3 Ω when the frequency increased from 20 Hz to 10,000 Hz.

EXPERIMENTAL STUDY ON PRESSURE SENSITIVE PROPERTIES OF COPPER CONTAMINATED SOIL SOLIDIFIED BY MODIFIED RED MUD

As a static method for testing pollution and strength of soil, the resistivity method has been used by many scholars, whereas few studies have been carried out on dynamic deformation monitoring by this method. To study the pressure sensitive properties of copper contaminated soils solidified by modified red mud, a series of unconfined compression tests were conducted. The compressive stress, strain and electrical resistivity in whole process were determined. Relationship between the resistivity and the parameters including stress, strain, red mud content, copper content, and curing age were analysed. Then the mechanism of electrical resistivity is revealed. Results indicate the stress-resistivity change rate follows the same trend as the stress-strain curve. The resistivity change rate follows the same rule as the strain change, indicating that the electrical resistivity can reflect the strain indirectly. The higher red mud content is, the better pressure sensitive properties of solidified soil is. A proper amount of copper can improve the pressure sensitivity of solidified soil, while excessive copper ions can reduce pressure sensitivity of solidified soil. These changes can be attributed to the pore water, iron oxide in red mud, tunnel conductive effect and conductivity percolation.